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Southern blot

A Southern blot is a laboratory method used to detect specific DNA molecules from among a many other DNA molecules. The technique was named after its inventor, Edward Southern. As a lab procedure, Southern blots can be used to analyze an organism's total DNA, also known as its genome, in order to identify a specific sequence of interest.

The first step in a Southern blot is to prepare the DNA mixture by breaking it into small fragments using a protein called a restriction enzyme. The mixture of DNA fragments is then separated according to size by way of a technique called gel electrophoresis. Following separation, the double-stranded pieces of DNA are denatured, or separated, into single strands within the gel. Next, the DNA is transferred from the gel onto a blotting membrane. Although this step is what gives the technique the name "Southern blotting," the term is typically used to describe the entire procedure.

Once the transfer is complete, the membrane carries all of the bands originally on the gel. The membrane is then treated with a small piece of DNA or RNA called a probe, which has been designed to have a sequence that is complementary to a particular DNA sequence in the sample; this allows the probe to hybridize, or bind, to a specific DNA fragment on the membrane. In addition, the probe has a label, which is typically a radioactive atom or a fluorescent dye. Thus, following hybridization, the probe permits the DNA fragment of interest to be detected from among the many different DNA fragments on the membrane.


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